This application claims priority to Japanese Patent Application No. 243380/2000, filed on Aug. 10, 2000 in Japan. The contents of the aforementioned application are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a control system and method and an engine control unit for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, and a two-stage fuel injection combustion mode in which the fuel injection into the cylinder is performed once during the intake stroke and once during the compression stroke during transition between the homogeneous combustion mode and the stratified combustion mode.
2. Description of the Prior Art
Conventionally, a fuel injection control system of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-82135. In this control system, the combustion mode of the engine is selected from the stratified combustion mode, the homogeneous combustion mode, and the two-stage fuel injection combustion mode, depending on the engine rotational speed and a target torque, and the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode so as to reduce torque steps. In the two-stage fuel injection combustion mode, a final fuel injection amount which is the sum total of two amounts of fuel to be injected during the compression stroke and during the intake stroke, respectively, is determined based on the intake air amount and the engine rotational speed, and one of the two amounts is set to a fixed amount, while the other is determined by subtracting the one amount (fixed amount) from the final fuel injection amount. Then, the fuel injection is performed during the compression stroke and during the intake stroke by using the one and the other amounts of fuel thus determined.
Further, another control system of the same kind has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-93731. An internal combustion engine incorporating this control system includes a swirl control valve for control of a swirl of fuel, and an EGR control valve for control of the EGR rate. In this control system as well, similarly to the above control system, the combustion mode of the engine is selected from the stratified combustion mode, the homogeneous combustion mode, and the two-stage fuel injection combustion mode, depending on the engine rotational speed and a target fuel injection amount (target torque). Further, the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode, and the duration period of the two-stage fuel injection combustion mode is determined based on a difference between a target value of the degree of opening of the swirl control valve and an actually detected value of the same.
A still another control system of the same kind has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-22508. Similarly to the above control system, this control system also selects the stratified combustion mode or the homogeneous combustion mode depending on the engine rotational speed and engine load, and the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode. In the two-stage fuel injection combustion mode, the target air-fuel ratio (equivalent ratio) is progressively changed between a rich value for the homogeneous combustion mode and a lean value for the stratified combustion mode by using a weighted mean value of the target air-fuel ratio. Further, the total fuel injection amount is divided into respective amounts of fuel for injections during the intake stroke and during the compression stroke such that a ratio between the divided amounts is also progressively changed, to thereby reduce torque steps.
Of the three conventional control systems described above, the first-mentioned control system sets one of the respective amounts of fuel to be injected during the compression stroke and during the intake stroke to a fixed value in the two-stage fuel injection combustion mode, and hence if an operating condition of the engine, particularly the engine rotational speed, has changed during this mode, the state of flow of air within the cylinder is changed to vary the minimum fuel injection amount in which injected fuel can be ignited during the compression stroke, which sometimes hinders an appropriate air-fuel mixture from being formed. As result, the state of combustion of the engine becomes unstable to cause undesired variation in the engine output, which degraded drivability and fuel economy.
Generally, when EGR control is executed, the EGR rate has a significant influence on the combustion of the mixture, and it is necessary to properly control the EGR rate to ensure the stability of combustion of the engine. Also, in general, so long as the torque demanded of the engine is identical, the degree of opening of a throttle valve and the EGR rate set by the EGR control valve are controlled to respective fairly larger values in the stratified combustion mode than in the homogeneous combustion mode, so that during transition from one of these modes to the other, it takes time for the EGR control valve controlled to a target valve lift amount for one of these combustion modes to be changed to a target value lift amount for the other. That is, the EGR control valve has the lowest response of all devices directly related to the fuel combustion of the engine, and at the same time the most significant influence thereon. The second-mentioned control system, however, merely determines the duration period of the two-stage fuel injection combustion mode based on the difference between the target value of the degree of opening of the swirl control valve and the actually detected value of the same, so that shortage or excess of the EGR rate due to delayed response of the EGR control valve can make the combustion unstable upon termination of the two-stage fuel injection combustion mode. This leads, similarly to the case of the first-mentioned control system, to degraded fuel economy, and degraded drivability due to undesired variation of the engine output.
Further, the third-mentioned conventional control system only progressively changes the target air-fuel ratio in the two-stage fuel injection combustion mode between the rich value suitable for the homogeneous combustion mode and the lean value suitable for the stratified combustion mode, so that when an operating condition of the engine has changed during the two-stage fuel injection combustion mode, the torque actually generated can deviate from a target torque. This causes torque steps upon termination of the two-stage fuel injection combustion mode, leading to degraded drivability.
It is an object of the invention to provide a control system and method and an engine control unit for an internal combustion engine, which are capable of properly determining an amount of fuel to be injected during a two-stage fuel injection combustion mode and a duration period of the two-stage fuel injection fuel combustion mode, such that stable combustion and smooth transition between combustion modes are ensured, thereby attaining excellent drivability and fuel economy.
To attain the above object, according to a first aspect of the invention, there is provided a control system for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, and a two-stage fuel injection combustion mode in which the fuel injection into the cylinder is performed once during the intake stroke and once during the compression stroke during transition between the homogeneous combustion mode and the stratified combustion mode.
The control system according to the first aspect of the invention is characterized by comprising:
a demanded torque-calculating module for calculating a demanded torque which is demanded of the engine;
an engine rotational speed-detecting module for detecting a rotational speed of the engine;
a combustion mode-determining module for determining, based on the calculated demanded torque, which of the homogeneous combustion mode, the stratified combustion mode, and the two-stage fuel injection combustion mode should be selected as the combustion mode; and
a fuel injection amount-determining module for determining an amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine.
According to this control system for an internal combustion engine, the combustion mode-determining module determines, based on the demanded torque which is demanded of the engine, which of the homogeneous combustion mode, the stratified combustion mode, and the two-stage fuel injection combustion mode should be selected as the combustion mode. Further, when the selected combustion mode is the two-stage fuel injection combustion mode, the amount of fuel to be injected during the compression stroke is determined by the fuel injection amount-determining module based on the rotational speed of the engine. This makes it possible to set the amount of fuel to be injected during the compression stroke in the two-stage fuel injection mode to the minimum amount in which the injected fuel can be ignited, while taking into account a change in the flow of air within the cylinder caused by a change in the rotational speed of the engine even when the change in the flow of air within the cylinder is caused. Conversely, it is possible to secure as long a fuel injection time period as possible for the intake stroke in which an air-fuel mixture in an easily flammable condition is produced. As a result, it is possible to ensure stable combustion of fuel injected in the two-stage fuel injection combustion mode, and excellent fuel economy and drivability.
To attain the above object, according to a second aspect of the invention, there is provided a control method for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, and a two-stage fuel injection combustion mode in which the fuel injection into the cylinder is performed once during the intake stroke and once during the compression stroke during transition between the homogeneous combustion mode and the stratified combustion mode.
The control method according to the second aspect of the invention is characterized by comprising the steps of:
calculating a demanded torque which is demanded of the engine;
detecting a rotational speed of the engine;
determining, based on the calculated demanded torque, which of the homogeneous combustion mode, the stratified combustion mode, and the two-stage fuel injection combustion mode should be selected as the combustion mode; and
determining an amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine.
This control method provides the same advantageous effects as described above concerning the control system according to the first aspect of the invention.
To attain the above object, according to a third aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out control of an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, and a two-stage fuel injection combustion mode in which the fuel injection into the cylinder is performed once during the intake stroke and once during the compression stroke during transition between the homogeneous combustion mode and the stratified combustion mode.
The engine control unit according to the third aspect of the invention is characterized in that the control program causes the computer to calculate a demanded torque which is demanded of the engine, detect a rotational speed of the engine, determine, based on the calculated demanded torque, which of the homogeneous combustion mode, the stratified combustion mode, and the two-stage fuel injection combustion mode should be selected as the combustion mode, and determine an amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine.
This engine control unit provides the same advantageous effects as described above concerning the control system according to the first aspect of the invention.
Preferably, the control system further includes a storage module for storing data of a fuel injection timing for the homogeneous combustion mode and a fuel injection timing for the stratified combustion mode, which are set in advance in a manner correlated to an operating condition of the engine, an operating condition-detecting module for detecting the operating condition of the engine, and a fuel injection timing-setting module for setting a fuel injection timing during the intake stroke and a fuel injection timing during the compression stroke in the two-stage fuel injection combustion mode, to the fuel injection timing for the homogeneous combustion mode and the fuel injection timing for the stratified combustion mode, respectively, in dependence on the detected operating condition of the engine.
According to this preferred embodiment of the control system, the fuel injection timing during the intake stroke and that during the compression stroke in the two-stage fuel injection combustion mode are set by the fuel injection timing-determining module to the fuel injection timing for the homogeneous combustion mode and that for the stratified combustion mode stored in the storage module, respectively, in dependence on the detected operating condition of the engine. This makes it possible to execute fuel injection during the intake stroke and that during the compression stroke in the two-stage fuel injection combustion mode at respective appropriate timings. Further, it is not necessary to separately or additionally provide a device for determining these fuel injection timings in the two-stage fuel injection combustion mode or software therefor, so that the manufacturing costs can be reduced by so much amount.
Preferably, the control method further includes the steps of storing data of a fuel injection timing for the homogeneous combustion mode and a fuel injection timing for the stratified combustion mode, which are set in advance in a manner correlated to an operating condition of the engine, detecting the operating condition of the engine, and setting a fuel injection timing during the intake stroke and a fuel injection timing during the compression stroke in the two-stage fuel injection combustion mode, to the fuel injection timing for the homogeneous combustion mode and the fuel injection timing for the stratified combustion mode, respectively, in dependence on the detected operating condition of the engine.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the control program further causes the computer to store data of a fuel injection timing for the homogeneous combustion mode and a fuel injection timing for the stratified combustion mode, which are set in advance in a manner correlated to an operating condition of the engine, detect the operating condition of the engine, and set a fuel injection timing during the intake stroke and a fuel injection timing during the compression stroke in the two-stage fuel injection combustion mode, to the fuel injection timing for the homogeneous combustion mode and the fuel injection timing for the stratified combustion mode, respectively, in dependence on the detected operating condition of the engine.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
More preferably, the control system further includes an ignition timing-determining module for determining ignition timing for the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine and the fuel injection timing for the stratified combustion mode.
As described hereinabove, while the engine rotational speed has a significant influence on the stability of combustion in the two-stage fuel injection combustion mode, the fuel injection timing during the compression stroke in the two-stage fuel injection combustion mode is the fuel injection timing for the stratified combustion mode. The fuel injected this time is involved in the ignition of the whole injected fuel. According to this preferred embodiment of the control system, the ignition timing-determining module determines the ignition timing in the two-stage fuel injection combustion mode based on the engine rotational speed and the fuel injection timing for the stratified combustion mode. This makes it possible to set the ignition timing such that stable or reliable ignition can be ensured in the two-stage fuel injection raw combustion mode, whereby further stable combustion can be ensured.
More preferably, the control method further includes the step of determining ignition timing for the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine and the fuel injection timing for the stratified combustion mode.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
More preferably, the control program further causes the computer to determine ignition timing for the two-stage fuel injection combustion mode, based on the detected rotational speed of the engine and the fuel injection timing for the stratified combustion mode.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
The engine includes an intake system, and preferably, the control system further includes an EGR control valve for controlling an EGR rate at which exhaust gases are recirculated into the intake system, and a duration period-determining module for determining a duration period of the two-stage fuel injection combustion mode, based on a parameter indicative of response of the EGR control valve.
According to this preferred embodiment of the control system, the duration period-determining module determines the duration period of the two-stage fuel injection combustion mode in dependence on a parameter indicative of the response of the EGR control valve. This enables the two-stage fuel injection combustion mode to be continued until the actual valve lift amount of the EGR control valve is positively changed such that it becomes substantially equal to the target valve lift amount of the EGR control valve set for a combustion mode following the present two-stage fuel injection combustion mode. As a result, the stable combustion can be ensured upon termination of the two-stage fuel injection combustion mode, whereby stable drivability in which the engine output variation is small can be ensured. Further, since the duration period of the two-stage fuel injection combustion mode is determined as described above, it can be reduced to the minimum necessary time period, whereby the degradation of fuel economy can be prevented.
The engine includes an intake system and an EGR control valve, and preferably, the control method further includes the steps of controlling an EGR rate at which exhaust gases are recirculated via the EGR control valve into the intake system, and determining a duration period of the two-stage fuel injection combustion mode, based on a parameter indicative of response of the EGR control valve.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
The engine includes an intake system and an EGR control valve, and preferably, the control program further causes the computer to control an EGR rate at which exhaust gases are recirculated via the EGR control valve into the intake system, and determine a duration period of the two-stage fuel injection combustion mode, based on a parameter indicative of response of the EGR control valve.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the fuel injection amount-determining module sets the amount fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode to a smaller valve as the rotational speed of the engine is higher.
Preferably, the step of determining the amount of fuel to be injected includes setting the amount fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode to a smaller valve as the rotational speed of the engine is higher.
Preferably, when the control program causes the computer to determine the amount of fuel to be injected, the control program causes the computer to set the amount fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode to a smaller valve as the rotational speed of the engine is higher.
More preferably, the control system includes an applied mode-changing module for causing a total amount of fuel for the two-stage fuel injection combustion mode to be injected at an injection timing for the stratified combustion mode, if a sum total of the amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode determined by the fuel injection amount-determining module and a predetermined fuel injection amount is equal to or smaller than the total amount of fuel.
More preferably, the control method includes the step of causing a total amount of fuel for the two-stage fuel injection combustion mode to be injected at an injection timing for the stratified combustion mode, if a sum total of the amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode determined by the step of determining the amount of fuel to be injected and a predetermined fuel injection amount is equal to or smaller than the total amount of fuel.
More preferably, the control program causes the computer to cause a total amount of fuel for the two-stage fuel injection combustion mode to be injected at an injection timing for the stratified combustion mode, if a sum total of the determined amount of fuel to be injected during the compression stroke in the two-stage fuel injection combustion mode and a predetermined fuel injection amount is equal to or smaller than the total amount of fuel.
More preferably, the homogeneous combustion mode comprises a stoichiometric combustion mode in which an air-fuel mixture having an air-fuel ratio equal to or richer than a stoichiometric air fuel ratio is burned, and a lean combustion mode in which an air-fuel mixture having an air-fuel ratio leaner than the stoichiometric air-fuel ratio is burned, and the fuel injection timing-setting module sets the fuel injection timing during the intake stroke in the two-stage fuel injection combustion mode to a fuel injection timing for the stoichiometric combustion mode when a combustion mode preceding the two-stage fuel injection combustion mode is the stoichiometric combustion mode, and to a fuel injection timing for the lean combustion mode when the combustion mode preceding the two-stage fuel injection combustion mode is other than the stoichiometric combustion mode.
More preferably, the homogeneous combustion mode comprises a stoichiometric combustion mode in which an air-fuel mixture having an air-fuel ratio equal to or richer than a stoichiometric air fuel ratio is burned, and a lean combustion mode in which an air-fuel mixture having an air-fuel ratio leaner than the stoichiometric air-fuel ratio is burned, and the step of setting the fuel injection timing includes setting the fuel injection timing during the intake stroke in the two-stage fuel injection combustion mode to a fuel injection timing for the stoichiometric combustion mode when a combustion mode preceding the two-stage fuel injection combustion mode is the stoichiometric combustion mode, and to a fuel injection timing for the lean combustion mode when the combustion mode preceding the two-stage fuel injection combustion mode is other than the stoichiometric combustion mode.
More preferably, the homogeneous combustion mode comprises a stoichiometric combustion mode in which an air-fuel mixture having an air-fuel ratio equal to or richer than a stoichiometric air fuel ratio is burned, and a lean combustion mode in which an air-fuel mixture having an air-fuel ratio leaner than the stoichiometric air-fuel ratio is burned, and when the control program causes the computer to set the fuel injection timing, the control program causes the computer to set the fuel injection timing during the intake stroke in the two-stage fuel injection combustion mode to a fuel injection timing for the stoichiometric combustion mode when a combustion mode preceding the two-stage fuel injection combustion mode is the stoichiometric combustion mode, and to a fuel injection timing for the lean combustion mode when the combustion mode preceding the two-stage fuel injection combustion mode is other than the stoichiometric combustion mode.
Preferably, the control system further includes an operation control values-setting module for setting at least a target air-fuel ratio, a target EGR rate, a fuel injection timing, and an ignition timing, in dependence on the combustion mode determined to be selected.
According to this preferred embodiment of the control system, the operation control values-setting module sets at least a target air-fuel ratio, a target EGR rate, a fuel injection timing, and an ignition timing, in dependence on the combustion mode determined to be selected, and therefore, by using these parameters, it is possible to control the two-stage fuel injection combustion mode and the combustion modes before and after the two-stage fuel injection combustion mode such that the torque generated by the engine becomes equal to the demanded torque. As a result, differently from the prior art, it is possible to prevent torque steps from being caused upon the start or the termination of the two-stage fuel injection combustion mode.
Preferably, the control method includes the step of setting at least a target air-fuel ratio, a target EGR rate, a fuel injection timing, and an ignition timing, in dependence on the combustion mode determined to be selected.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the control program causes the computer to set at least a target air-fuel ratio, a target EGR rate, a fuel injection timing, and an ignition timing, in dependence on the combustion mode determined to be selected.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
The engine includes a fuel injection valve for injecting the fuel into the cylinder, the cylinder having a top wall facing a combustion chamber, and preferably, the fuel injection valve is arranged in a central portion of the top wall such that the fuel injection valve injects the fuel downward therefrom.
According to this preferred embodiment, the advantageous effects by the control system and method and the engine control unit according to the respective aspects of the invention and their preferred embodiments described above can be obtained in an optimized manner.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.